Cartridge case rim gauge



March 22, W49. D. F. WINDNAGLE CARTRIDGE QASE RIM GAUGE Filed March 7,194'? Patented Mar. 22, 1949 UNITED STAT S TENT OFFICE 6 Claims.

Thi invention relates to gauges, and more particularly to such devicesas may be used to measure the thickness of a cartridge case rim.

A rim fire cartridge has the priming material located only in the rim ofthe cartridge case head. It has been found that in productionmanufacture the thickness of the rim varies sometimes as much as .007inch. The space provided in a rifle for this rim is called head space."It has been found that with the same elevation of aim there are varyingelevations of bullet impact at the target as the thickness of thecartridge rim varies. Sometimes, however, it is found that a certain rimthickness produces much more accurate fire in certain rifles than inothers. Some rifles will shoot cartridges of various rim thicknesses andhold a constant elevation of impact on the target as long as cartridgesof the same rim thicknesses are used.

There is often a quarter of an inch difference in elevation of impact atthe 100-yard target for a variation of .001 inch in the cartridge rimthickness.

It has also been found that cartridges in which the bullet is notconcentric with respect to the cartridge casing will cause deflectionwhen shot and, therefore, inaccurate target impact.

The object of this invention is, therefore, to provide a simple,inexpensive and effective gauge whereby rim thicknesses of a given lotof cartridges may be accurately measured or compared and thereby permitthe cartridges to be segregated according to size.

A further object of this invention is to provide a simple and effectiveadjustment in a dea vice of the nature herein described whereby lack ofaccuracy due to natural wear may be conveniently remedied.

A further object is to provide in this device means whereby theirregularities often occurring on cartridge heads may not affect theaccurate determination of the vital thickness of the cartridge rim.

A further object is to provide in this device means whereby cartridgescontaining bullets not concentrically seated with respect to thecartridge casing will provide an indication that they are faulty.

The above and still further objects of the invention will becomeapparent from the following description when taken in conjunction withthe accompanying drawings, the invention being pointed out in theappended claims.

Reference is made to the drawings wherein like numerals of referenceapply to the same parts throughout the several views, and wherein:

Figure 1 is a plan view of the device with a cartridge in place fordetermination of its rim thickness,

Figure 2 is an elevational view,

Figure 3 is a sectional elevation taken on lines 3-3 of Figure 2, and

Figure 4 is a bottom view of the dial member and supporting screw withwhich it rotates.

Referring to the drawings in detail, in Figures 1, 2 and 3, a circularbase plate ll! of suitable material, such as, for example, steel, isprovided with a centrally located tapped hole H. A narrow slot l2terminating in a hole I3 is provided from one edge across the face ofthe base plate It for a distance equal to about threequarters of itsdiameter and a portion of the periphery is cut away to provide a seat Mfor adjusting screw l5 which operates in tapped hole ii and serves todraw together the two portions of the slotted base plate In in orderthat wear on the threads in tapped hole H may be taken up andinaccuracies avoided in its micrometer-like action.

A hole containing a bushing I8 is provided adjacent the periphery ofbase plate ID in which the cartridge l9 to be measured is thrust. Thisbushing is very accurately bored to nicely fit the normal outsidediameter of a perfect cartridge, and yet allow it to be readily insertedor removed. In the event an attempt is made to in sert in the bushing l8an imperfectly assembled cartridge, such as one whose bullet is notconcentric with the cartridge shell, the body of the cartridge will notreadily enter the bushing and be properly seated for measurement of thethickness of its rim, because of the unsymmetry of its body and may,therefore, be discarded as imperfect. This is the first step indetermination of the perfection of the cartridge, as unsymmetricalcartridges will cause deflection of the bullet when fired.

A micrometer dial shaft provided with a lower threaded portion isadapted to snugly fit and rotate in the tapped hole I l is also providedwith a shoulder 20 and has its upper end threaded to fit a tapped thumbknob 2|. A dial 22 is seated on the shoulder 20 and secured for rotationwith the dial shaft by tightening the thumb knob 2| and thus forcingtogether the dial 22 and shoulder 20 to a locked friction fit. A slot19a (Figure 4) is provided in the lower end of the dial shaft to permitinsertion of a holding tool, while the thumb knob 2! is rotated intolocking position with the dial 22.

Dial 22 is of such diameter as will normally cover the head of thecartridge [9, but has a portion 23 of its diameter cut away so that itmay be rotated to suitable position that a car tridge may be readilyinserted in or removed from the bushing l8.

The outer diametrical edge 22a of the dial 22 is chamfered and numberedgraduations stamped thereon to correspond with the index line 24 locatedon the base plate opposite the cartridge bushing l8, and thus determinethe thickness or comparative thickness, of the rim of the cartridge whenthe dial 22 is properly rotated until its under side contacts the headof the cartridge.

Many cartridges have identification letters, symbols or numerals stampedon their heads, such as, for example, the X shown on the head of thecartridge IS in Figure 1. These stampings may cause burs orirregularities on the top of the cartridge which will affect theaccuracy determination of the rim thickness; a suitably shaped slot 26has, therefore, been cut in the under side surface of the dial 22 havinga radius and width which permit the stamped symbol to be straddled andonly the perfect edge of the rim contacted by the finished under surfaceof the dial.

A short length chamfer 25 has been provided on the under edge of thestraight portion of the dial to avoid abrupt contact with the cartridgewhen the dial is rotated and about to contact its run.

It will be readily seen that bushings of different internal diametersmay be inserted in the bushing hole and thus cartridges of differentdiameters or sizes measured.

It is to be understood that various modifications and changes may bemade in this invention without departing from the spirit and scopethereof as set forth in the appended claims.

What is claimed is:

1. A cartridge rim-measuring device comprising a base containing a screwthread, a rotatable threaded shaft cooperating with said screw threadand provided with a dial adapted to be rotated with said shaft intocontact with the head of a cartridge, a hole in said base containing abushing adapted to support said cartridge to be measured, and means onsaid dial adapted to indicate the thickness of the rim of said cartridgewhen said dial is rotated with said shaft on said threads,

2. A cartridge rim-measuring device comprising a base containing a screwthread, a rotatable threaded shaft cooperating with said screw threadand provided with a dial adapted to be rotated with said shaft intocontact with the head of a cartridge, a hole in said base adapted tosupport cartridges of different diameters to be measured, and means onsaid dial adapted to indicate the thickness of the rim of said cartridgewhen said dial is rotated with said shaft on said threads.

3. A cartridge rim-measuring device comprising a base containing a screwthread, means for regulating the diameter of said screw thread, arotatable threaded shaft cooperating with said screw thread and providedwith a dial adapted to be rotated with said shaft into contact with thehead of a cartridge, a hole in said base containing a bushing adapted tosupport said cartridge to be measured, and means on said dial adapted toindicate the thickness of the rim of said cartridge when said dial isrotated with said shaft on said threads.

4. A cartridge rim-measuring device comprising a base containing a screwthread, a rotatable threaded shaft cooperating with said screw threadand provided with a dial adapted to be rotated with said shaft intocontact with the head of a cartridge, a hole in said base containing abushing adapted to support said cartridge to be measured, andgraduations on said-dial cooperating with an index line on said base toindicate the thickness of the rim of said cartridge when said dial isrotated with said shaft on said threads.

5. A cartridge rim-measuring device comprising a base containing a screwthread, a rotatable threaded shaft cooperating with said screw threadand provided with a dial adapted to be rotated with said shaft intocontact with the head of a cartridge, a hole in said base containing abushing adapted to support a cartridge to be measured, and a coaxiallydisposed depression in the cartridge-contacting surface of said dialadapted to straddle irregularities on the head of said cartridge whensaid dial is rotated.

6. A cartridge rim measuring device comprising a base, means associatedwith said base including a dial adapted to be rotated into contact withthe head of a cartridge, said base including a hole containing a bushingadapted to support a cartridge to be measured, and means associated withsaid first-mentioned means permitting said firstmentioned means tocontact the rim of said cartridge only, straddling the insignia thereon.

DEWEY F. WINDNAGLE.

No reference cited.

